Dehydrofluonnation

MonofluoToalkanes and vicinal difluoroalkanes are dehydrofluonnated if strong enough bases are applied [10 12] In 5-fluorononane and fluorocyclodo-decane, elimination by means of sodium methoxide in methanol gives cis- and trans allcenes in respective yields of 8 and 21% and in ratios of 1 2 2 2 4, however, the bulky lithium diisopropyl amide m tetrahydrofuran produces trdns-isomers almost exclusively The strength of the base does not have much effect on the rate of elimination, but the lithium cation causes considerable acceleration [10] (equation 10)... 

The ratios of the rates of elimination of hydrogen halides depend evidently on the structure of the halogenated compound and span many orders of magnitude The rate of dehydrofluonnation w much slower than that of dehydrochlonnation, dehydrobromination and dehydrolodination However, there are exceptions... 

Defluorination occurs even with sodium fluoride at 530 °C when tetra-fluorothiolene is converted to 2,5-difluQrothiophene [63], Dehydrofluonnation would be expected at such high temperature, but defluonnation is favored. The product composition also excludes a disproportionation reaction mechanism (equation 32). 

Dehydrofluorination by primary and secondary aliphatic amines occurs at room temperature and is the basis of diamine cross linkmg, which occurs by dehydrofluonnation and subsequent nucleophihc substitution of the double bond The locus of dehydrofluonnation is a VDF unit flanked by two perfluoroolefin units This selectively base-sensitive methylene group also undergoes elimination as the first step in phase-transfer-catalyzed cross-hnking with quaternary ammo mum or phosphomum salts, bisphenols, and morganic oxides and hydroxides as HF acceptors [31, 32]... 

Most aliphatic [95, 184, 185, 186, 187], aromatic [95 186,188], and heterocyclic [189,190] ketones react with DAST in the usual way to give geminal difluoro derivatives Fluorination of cycloaliphatic ketones, in particular, is often accompanied by a spontaneous dehydrofluonnation to form considerable amounts of... 

Dehydrofluonnation of compounds in which a single hydrogen is flanked by heavily fluorinated groups is achieved by aqueous or alcoholic alkali hydroxides and proceeds probably by theElcB mechanism Thus 1 -(2//-hexafluoropropyl)ada-mantane [25] and 1,3 bis(2// hexafluoropropy])adamantane [16] are dehydro-fluorinated in respective yields of 75 and 81% (equation 14)... 

Polyfluorocyclohexanes are dehydrofluonnated by potassium hydroxide to polyfluorocyclohexenes and polyfluorocyclohexadienes (where applicable) The reaction is sometimes very complex [17] (equation 15)... 

Dehydrofluonnation of dihydrododecafluorocycloheptanes gives a mixture of monohydroundecafluorocycloheptenes and decafluorocycloheptadienes [18] (equation 16)... 

Similar dehydrofluonnation occurs with polyfluorinated heterocycles. 2,2-Bis(tnfluoromethyl)-3,4-difluorooxetane gives 3-fluoro-4,4-bis(trifluoromethyl)-2-oxete [19] (equation 17), and heptafluoro-p-dioxane yields hexafluoro-p dioxene [20] (equation 18)... 

A peculiar dehydrofluonnation occurs when tnfluoromethyl dihydropyndine derivatives are treated with organic bases A double-bond shift and a hydrogen migration convert one tnfluoromethyl group to a difluoromethyl group and aromatize the ring [22] (equation 20)... 

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